1. Field of the Invention
The present invention relates to a light-transmitting module.
2. Related Prior Art
A laser diode (LD) is controlled in its temperature to emit light with a predetermined wavelength. Generally, the control of the temperature is performed by using a Peltie device, on which the LD is installed. Such configuration is disclosed in Japanese patent published by 2000-252576 and 61-215381.
The light-emitting module is assembled by installing the LD and Peltier device in the package, and the light-transmitting module includes such light-emitting module and a substrate on which various electronic components are mounted to control the LD and the Peltier device in the light-emitting module.
Generally, when the LD is operated, the temperature of the light-transmitting module rises due to the self-heating. Therefore, to keep the temperature of the LD to emit light at a predetermined wavelength, the LD should be cooled down by the Peltier device. However, when an ambient temperature is lower than the preset temperature of the LD, for example, the ambient temperature of the module is below the freezing point while the preset temperature of the LD is the room temperature, then the LD should be heated up. When the upper surface of the Peltier device, where the LD is mounted thereon, is heated up, the lower surface of the Peltier device is cooled down due to the Peltier effect.
However, in the case that the temperature of the package is lowered, the condensation may be brought in the outer surface of the package. The condensation causes the short circuit and the breaking of the wiring on the substrate, especially in the light-transmitting module having a hot plug configuration, the droplets of the condensation causes the trouble of the electrical connector. Therefore, the light-transmitting module can not emit light in stable and reliable.
Accordingly, one object of the present invention is to provide a light-transmitting module that enables to output light in stable and reliable even under a condition that an ambient temperature is lower than a preset temperature of the light-emitting device.